Rowing with a spatiotemporally asymmetric paddle at intermediate Reynolds numbers

Metachronal rowing is a locomotive strategy widely used by animals that swim at intermediate Reynolds numbers (e.g., krill, shrimp, etc.). It consists of creating thrust by the sequential beating of a row of closely spaced paddles. This thrust is obtained by two kinematic mechanisms: spatial asymmetry (Sa, i.e., differing paddle flow-normal area between power vs. recovery strokes) and temporal asymmetry (Ta, i.e., differing duration between power vs. recovery strokes). However, the combined effect of Sa-Ta on flow production at intermediate Reynolds numbers (Re) is not fully understood, particularly for highly deformable structures. We designed a dynamically scaled compliant propulsor capable of mimicking the spatiotemporal asymmetries of the beat cycle observed in ctenophores. A flexible paddle is connected to a motor at the base, which controls the stroke's Ta and the overall Re. The Sa of the stroke is encoded into the structure and geometry of the paddle. This construction allows us to explore the flows generated by spatiotemporally asymmetric, flexible paddles across a range of intermediate Re. Improving our understanding of metachronal rowing at intermediate Re could lead to the design of bioinspired sensors, pumps, or mixers for micro-fluidic platforms.